For HVDC (High Voltage DC) networks, suitable topologies for DC grid interconnectors are being sought, using suitable high voltage DC/DC converters.
WO 2011/029566 A1 discloses DC/DC converter units. Each DC/DC converter unit consists of a conventional full H bridge DC/AC converter block employing suitable power semiconductor switching devices and a diode bridge which operates as a passive rectifier. The DC/AC and AC/DC converter blocks and are provided on each side of a medium or high frequency transformer which provides galvanic isolation. The DC/DC converter units will normally be configured for unidirectional power flow (i.e. from the ac supply network to subsea electrical loads) and there is no requirement for the AC/DC converter block to provide an inverter function.
However, the structure of the presented DC/DC converter is complicated and can only be increased in capacity by adding more links from DC to AC to DC.